Composition and recording sheet with improved optical properties

ABSTRACT

A composition is provided, which comprises a water-soluble salt of a divalent metal; a complexing agent having an affinity for the divalent metal; and an optical brightening agent. Methods of using the composition, and recording sheets which include the composition, are also disclosed.

BACKGROUND

1. Field of the Invention

This invention relates to compositions for use in papermaking. Theinvention also relates to methods of making and using paper products,for example, recording sheets, which include the composition.

2. Discussion of the Background

The demand in the marketplace is increasing for recording sheets,printing papers, writing papers, and the like which have superiorprinting and optical properties. To improve brightness and whiteness,for example, optical brighteners (OBAs) are being used in largeramounts. The OBAs are expensive, however, and their increased usecontributes substantially to higher product costs.

To improve printing properties such as ink density and dry time,cationic metals have been used. Calcium chloride is currently used inink jet recording media to enhance inkjet print density and dry time.See, for example, U.S. Patent Application Publication 2007/0087138,published on Apr. 19, 2007, which discloses a recording sheet withimproved image dry time which contains water soluble divalent metalsalts. Other metal salts have been used in inkjet recording media. U.S.Pat. No. 4,381,185 discloses paper stock which contains polyvalent metalcations. U.S. Pat. No. 4,554,181 discloses an ink jet recording sheethaving a recording surface which includes a water soluble polyvalentmetal salt. U.S. Pat. No. 6,162,328 discloses a paper sizing for ink jetprinting substrate that includes various cationic metal salts. U.S. Pat.No. 6,207,258 discloses a surface treatment composition for an ink jetprinting substrate which contains a divalent metal salt. U.S. Pat. No.6,880,928 discloses an ink jet recording base paper having a coatingwhich includes a polyvalent metal salt. It has been found, however, thatmany of these cationic additives decrease the brightness and whiteness.Calcium chloride, for example, undesirably quenches stilbene-basedoptical brighteners such as often used at the size press. Overcomingthis decrease in brightness and whiteness imposes additional costs onthe papermaking process.

Another disadvantage is that the use of certain cationic additives, suchas calcium chloride can create runnability issues in paper machines; andcalcium chloride affects the pH of size press formulations. Starchesused at the size press require a narrow pH range to be effective: toohigh of a pH may result in the yellowing of the starch; too low of a pHmay cause the starch to precipitate and/or gel. Calcium chloride canalso interact with other chemicals such as those used in the wet endwhen the paper is broked or recycled.

Synergistic mixtures of complexing agents, such as the known chelant,diethylenetriaminepentakis(methyl)phosphonic acid (DTPA), andpolyacrylic acid have been used to enhance brightness in chemical andmechanical pulps. See, for example, U.S. Pat. No. 7,351,764. Chelatingagents have also been used to produce acid-stabilized calcium carbonateslurries. See, e.g., U.S. Pat. No. 7,033,428. U.S. Patent ApplicationPublication 2007/0062653 discloses that the use of reducing agents incombination with certain chelants enhance the brightness of a paperproduct via increased thermal stability of the pulp and reduction ofchromophoric structures in pulp. There, it is disclosed that chelantsinclude compounds that are capable of chelating transitional metals thatform colored products with pulp constituents and catalyze color-formingreactions in the bleached pulp or paper products.

There is thus a need for a recording sheet with improved opticalproperties yet which reduces the costs associated with OBAs.

SUMMARY

The above problems, and others, are solved by the present invention.Quite surprisingly, the present inventors have found that a composition,comprising a water-soluble salt of a divalent metal, a complexing agenthaving an affinity for the divalent metal, and an optical brighteningagent inheres several advantages. When used in a papermaking process,one embodiment of the present invention improves the optical propertiessuch as whiteness and brightness of the paper product. In a recordingsheet, another embodiment of the present invention exhibits improvedoptical properties while desirably maintaining the beneficial printingproperties. It has also been found that another embodiment of thepresent invention desirably avoids precipitation and other runnabilityissues in the papermaking process.

BRIEF DESCRIPTION OF THE DRAWINGS

Various embodiments of the present invention are described inconjunction with the accompanying drawings, in which:

FIG. 1 shows graphical data of several inventive and comparativeembodiments and their effects on whiteness.

FIG. 2 shows graphical data of several inventive and comparativeembodiments and their effects on whiteness.

FIG. 3 shows graphical data of several inventive and comparativeembodiments and their effects on ink density.

FIG. 4 shows graphical data of several inventive and comparativeembodiments and their effects on ink removal.

FIG. 5 shows graphical data of several inventive and comparativeembodiments and their effects on whiteness.

FIG. 6 shows graphical data of several inventive and comparativeembodiments and their effects on whiteness.

FIG. 7 shows graphical data of several inventive and comparativeembodiments and their effects on TAPPI brightness.

FIG. 8 shows graphical data of several inventive and comparativeembodiments and their effects on whitness.

FIG. 9 shows graphical data of several inventive and comparativeembodiments and their effects on brightness.

FIG. 10 shows graphical data of several inventive and comparativeembodiments and their effects on brightness.

FIG. 11 shows tabular data of several inventive and comparativeembodiments and their effects upon UV and daylight aging.

FIG. 12 shows graphical data of several inventive and comparativeembodiments and their effect upon UV and daylight aging.

DETAILED DESCRIPTION OF THE SEVERAL EMBODIMENTS

One embodiment of the present invention desirably achieves improvedoptical properties with lower amounts of optical brighteners. Anotherembodiment of the present invention desirably achieves improved ink andprinting properties. Another embodiment of the present inventiondesirably achieves improved optical properties and improved ink andprinting properties. Another embodiment of the present inventiondesirably achieves improved paper machine runnability. Anotherembodiment of the present invention desirably achieves improved opticalproperties and improved machine runnability. Another embodiment of thepresent invention desirably achieves improved ink and printingproperties and improved machine runnability. Another embodiment of thepresent invention desirably achieves improved optical properties, inkand printing properties, and improved runnability. Another embodiment ofthe present invention desirably achieves ink fastness.

One embodiment relates to a composition, which comprises:

a water-soluble salt of a divalent metal;

a complexing agent having an affinity for the divalent metal; and

an optical brightening agent.

Another embodiment relates to a method for making a recording sheet,comprising contacting:

a paper substrate comprising a plurality of cellulosic fibers; and

a composition, comprising:

-   -   a water-soluble salt of a divalent metal;    -   a complexing agent having an affinity for the divalent metal;        and    -   an optical brightening agent;

to produce a recording sheet.

Another embodiment relates to a method, comprising:

forming an image with a printing apparatus on a surface of a recordingsheet, said recording sheet comprising:

a paper substrate comprising a plurality of cellulosic fibers; and

a composition, comprising:

-   -   a water-soluble salt of a divalent metal;    -   a complexing agent having an affinity for the divalent metal;        and    -   an optical brightening agent.

Another embodiment relates to a recording sheet, comprising:

a paper substrate comprising a plurality of cellulosic fibers; and

a composition, comprising:

-   -   a water-soluble salt of a divalent metal;    -   a complexing agent having an affinity for the divalent metal;        and    -   an optical brightening agent.

The composition includes at least one divalent metal salt. When used ina recording sheet, the recording sheet may suitably contain an effectiveamount of the divalent water soluble metal salt in contact with at leastone surface of the substrate. As used herein, an “effective amount” isan amount which is sufficient to obtain a good dry time or printingproperty. This total amount of divalent water soluble metal salt in thesubstrate can vary widely, provided that the desired result ismaintained or achieved. Usually, this amount is at least 0.02 g/m²,although lower or higher amounts can be used. The amount of divalentwater soluble metal salt is preferably from about 0.02 g/m² to about 4g/m², which ranges includes all values and subranges therebetween,including 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09, 0.1, 0.2, 0.3,0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1, 1.5, 2, 2.25, 2.5, 2.75, 3, 3.25, 3.5,3.75, and 4 g/m² or any combination thereof, and most preferably fromabout 0.04 g/m² to about 2.0 g/m². In one embodiment, the amount ofdivalent water soluble metal salt is preferably from about 0.04 g/m² toabout 1.5 g/m².

Any water soluble divalent metal salt can be used in the practice ofthis invention. Suitable divalent water soluble metal salts include butare not limited to compounds containing divalent calcium, magnesium,barium, zinc, or any combination of these. The counter ions (anions) maybe simple or complex and may vary widely. Illustrative of such materialsare calcium chloride, magnesium chloride, calcium acetate, calciumlactate, calcium EDTA, Mg EDTA, and the like, and combinations thereof.Preferred divalent water soluble metal salts for use in the practice ofthis invention are water soluble calcium salts, especially calciumchloride.

In one embodiment, the divalent metal salt may be a mineral or organicacid salt of a divalent cationic metal ion, or a combination thereof. Inone embodiment, the water soluble metal salt may include a halide,nitrate, chlorate, perchlorate, sulfate, acetate, carboxylate,hydroxide, nitrite, or the like, or combinations thereof, of calcium,magnesium, barium, zinc(II), or the like, or combinations thereof. Someexamples of divalent metal salts include, without limitation, calciumchloride, magnesium chloride, magnesium bromide, calcium bromide, bariumchloride, calcium nitrate, magnesium nitrate, barium nitrate, calciumacetate, magnesium acetate, barium acetate, calcium magnesium acetate,calcium propionate, magnesium propionate, barium propionate, calciumformate, calcium 2-ethylbutanoate, calcium nitrite, calcium hydroxide,zinc chloride, zinc acetate, and combinations thereof. Mixtures orcombinations of salts of different divalent metals, different anions, orboth are possible. The relative weight of the divalent cationic metalion in the divalent metal salt may be maximized, if desired, withrespect to the anion in the salt to provide enhanced efficiencies basedon the total weight of applied salt. Consequently, for this reason, forexample, calcium chloride may be preferred over calcium bromide.Equivalent performance in ink and print properties is expected whenequivalent dosages of divalent metal cations in the divalent metal saltsare present in the paper, expressed on a molar basis.

In one embodiment, one or more divalent metal salts are used.

In one embodiment, the divalent metal salt is soluble in the amount usedin an aqueous sizing formulation. In one embodiment, it is soluble atabout pH 6 to about pH 9. The aqueous sizing medium may be in the formof an aqueous solution, emulsion, dispersion, or a latex or colloidalcomposition, and the term “emulsion” is used herein, as is customary inthe art, to mean either a dispersion of the liquid-in-liquid type or ofthe solid-in-liquid type, as well as latex or colloidal composition.

In one embodiment, the water solubility of the divalent metal salt maysuitably range from slightly or moderately soluble to soluble, measuredas a saturated aqueous solution of the divalent metal salt at roomtemperature. The water solubility may range from 0.01 mol/L and upwards.This range includes all values and subranges therebetween, including0.01, 0.05, 0.1, 0.5, 1, 1.5, 2, 5, 7, 10, 15, 20, 25 mol/L and higher.In one embodiment, the water solubility of the divalent metal salt is0.1 mol/L or greater.

The composition contains one or more complexing agents. So long as ithas an affinity for the divalent metal (ion), the complexing agent isnot particularly limited. In this regard, the complexing agent may beany compound, molecule, or the like that has a chemical, physical, orphysicochemical affinity for the divalent metal. Examples of suchaffinities include, but should not be considered to be limited tochelation, electron donation, Van der Waals attraction, physisorption,chemisorption, ion-pairing, ionic, electrostatic, metal-ligand, steric,and the like. The affinity may be reversible or irreversible. In oneembodiment, the affinity results in an association between thecomplexing agent and the divalent metal, to form an associated complex.

The associated complex may be neutrally charged, or it may have apositive or slightly positive charge. The associated complex may arisefrom any number of divalent metal ions associated with any number ofcomplexing agents. The ratio of metal to complexing agent may suitablyrange from 10:1 to 1:10, or any value or subrange therebetween,including any one of 10, 9, 8, 7, 6, 5, 4, 3, 2, 1 to any one of 1, 2,3, 4, 5, 6, 7, 8, 9, 10.

In one embodiment, the water solubility of the associated complex thatresults from the association may suitably range from slightly ormoderately soluble to soluble, measured as a saturated aqueous solutionof the associated complex at room temperature. The water solubility mayrange from 0.01 mol/L and upwards. This range includes all values andsubranges therebetween, including 0.01, 0.05, 0.1, 0.5, 1, 1.5, 2, 5, 7,10, 15, 20, 25 mol/L and higher. In one embodiment, the water solubilityof the associated complex is 0.1 mol/L or greater.

The associated complex may be colorless or it may have color. It may beadvantageous in some applications that the associated complex is bothwater-soluble and colorless.

In one embodiment the associated complex is compatible with the opticalbrightening agent either in the solution phase or in the solid phase, orboth. So long as there is some association and/or interaction betweenthe complexing agent and the divalent metal, the nature of the affinityis not particularly limited.

Without wishing to be bound by theory, it is hypothesized that thecomplexing agent may “encage” the divalent metal ion while still leavingsome excess positive charge on the metal ion which will contribute togood ink fixation. It is also possible that complex cage-typeassociations, which contain sufficient organic molecular surfaces, wouldbe more compatible with the optical brightening agent (for examplepreventing the optical brightening agent from precipitating fromsolution) than the metal ion alone would be with the optical brighteningagent.

In one embodiment, the complexing agent may include one or more electrondonating atoms such as nitrogen, oxygen, phosphorus, sulfur, and thelike.

Some examples of complexing agents include organic phosphonate,phosphate, carboxylic acid, dithiocarbamate, EDTA salt, EGTA salt, DTPAsalt, crown ether, EDTA (CAS 60-00-4), EDTA disodium salt [6381-92-6],EDTA tetrasodium salt [194491-31-1], EDTA trisodium salt, EDTA disodiummagnesium salt [14402-88-1], EDTA disodium calcium salt, EDTA diammoniumsalt [20824-56-0], EDTA dipotassium salt [25102-12-9], EDTA tripotassiumsalt [65501-24-8], EDTA dilithium salt [14531-56-7], EDTAtetramethylammonium salt, EDTA calcium salt, EDTA magnesium salt, EDTAaluminum salt, polyacrylic acid, polyacrylic acid salt, polysorbate,poly-4-styrene sulfonic acid salt, glycerol formal, formamidinesulinicacid, sodium hypophosphite, potassium hypophosphite, calciumhypophosphite, organic phosphonate, organic phosphate, carboxylic acid,dithiocarbamate, sorbitol, sorbic acid, cellulose ether, CMC cellulose,hydroxyethyl cellulose, PEG, PEG derivatives, PPG, PPG derivatives,ionic liquids, 1-butyl-3-methyl-imidazolium-thiocyanate, and saltsthereof. Combinations are possible.

Examples of ionic liquids include those based on alkyl imidazolium, ie.methyl imidazolium (such as from BASF) and phosphonium salts (such asfrom Cytec). The anions could be halides, sulfates or alkyl sulfates,tetrachloroaluminate, acetate, thiocyanates, salicylates,hexafluorophosphates, hexafluoroborates, dioctylsulfosuccinate,decanoate, dodecylbenzenesulfonate. Further common examples of alkylimidazoliums may include, but are not limited to,1-ethyl-3-methylimidazolium thiocyanate, 1-ethyl-3-methylimidazoliumacetate, 1-ethyl-3-methylimidazolium methyl sulfate,1-butyl-3-methylimidazolium thiocyanate (or acetate, or methyl sulfate,or ethyl sulfate).

In some embodiments, it may be advantageous to use EDTA (CAS 60-00-4),EDTA disodium salt [6381-92-6], EDTA tetrasodium salt [194491-31-1],EDTA trisodium salt, EDTA disodium magnesium salt [14402-88-1], EDTAdisodium calcium salt, either alone, or in combination, as thecomplexing agent.

In one embodiment, the term, “organic phosphonate” may refer to organicderivatives of phosphonic acid, HP(O)(OH)₂, containing a single C—Pbond, such as HEDP (CH₃C(OH)(P(O)(OH)₂),1-hydroxy-1,3-propanediylbis-phosphonic acid((HO)₂P(O)CH(OH)CH₂CH₂P(O)(OH)₂)); preferably containing a single C—Nbond adjacent (vicinal) to the C—P bond, such as DTMPA((HO)₂P(O)CH₂N[CH₂CH₂N(CH₂P(O)(OH)₂)₂]₂), AMP (N(CH₂P(O)(OH)₂)₃), PAPEMP((HO)₂P(O)CH₂)₂NCH(CH₃)CH₂(OCH₂CH(CH₃))₂N(CH₂)₆N(CH₂P(O)(OH)₂)₂), HMDTMP((HO)₂P(O)CH₂)₂N(CH₂)₆N(CH₂P(O)(OH)₂)₂), HFEBMP(N(CH₂P(O)(OH)₂)₂CH₂CH₂OH), salts thereof, and the like. Combinationsare possible.

In one embodiment, the term, “organic phosphates” may refer to organicderivatives of phosphorous acid, P(O)(OH)₃, containing a single C—Pbond, including triethanolamine tri(phosphate ester)(N(CH₂CH₂OP(O)(OH)₂)₃), salts thereof, and the like. Combinations arepossible.

In one embodiment, the term, “carboxylic acids” may refer to organiccompounds containing one or more carboxylic group(s), —C(O)OH,preferably aminocarboxylic acids containing a single C—N bond adjacent(vicinal) to the C—CO₂H bond, such as EDTA((HO₂CCH₂)₂NCH₂CH₂N(CH₂CO₂H)₂), DTPA((HO₂CCH₂)₂NCH₂CH₂N(CH₂CO₂H)CH₂CH₂N(CH₂CO₂H)₂), and the like andalkaline and alkaline earth metal salts thereof. Combinations arepossible.

In one embodiment, the term, “dithiocarbamates” may refer to monomericdithiocarbamates, polymeric dithiocarbamates, polydiallylaminedithiocarbamates, 2,4,6-trimercapto-1,3,5-triazine, disodiumethylenebisdithiocarbamate, disodium dimethyldithiocarbamate, saltsthereof, and the like. Combinations are possible.

In one embodiment, the complexing agent is a phosphonate. In oneembodiment, the phosphonate is diethylene-triamine-pentamethylenephosphonic acid (DTMPA) and salts thereof.

In one embodiment, the complexing agent is a carboxylic acid. In oneembodiment, the carboxylate is selected fromdiethylenetriaminepentaacetic acid (DTPA) and salts thereof andethylenediaminetetraacetic acid (EDTA) and salts thereof.

In one embodiment, the complexing agent is one or more ionic liquids. Anexample of an ionic liquid is 1-butyl-3-methyl-imidazolium-thiocyanate.In another embodiment, the complexing agent is a combination of an ionicliquid and another (non ionic liquid) complexing agent.

The amount of complexing agent is not particularly limiting. When starchis used in a sizing formulation, the complexing agent may be present inan amount ranging from about 0.01 Lb/100 Lb starch to about 100 Lb/100Lb starch. This range includes all values and subranges therebetween,including about 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09,0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 10, 15, 20, 25, 30, 35, 40,45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95, 99, and 100 Lb complexingagent/100 Lb starch. If no starch is used, then the complexing agent maybe present in an amount ranging from about 0.01 Lb/ton of paper to about100 Lb/ton of paper. This range includes all values and subrangestherebetween, including about 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.07,0.08, 0.09, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 10, 15, 20, 25,30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95, 99, and 100 Lbcomplexing agent/ton of paper. In one embodiment, the amount ofcomplexing agent ranges from about 0.1 to about 10 Lbs/ton of paper.

The composition contains one or more optical brightening agents,sometimes referred to herein as optical brighteners or OBAs. Typically,the optical brightening agents are fluorescent dyes or pigments thatabsorb ultraviolet radiation and reemit it at a higher wavelengths inthe visible spectrum (blue), thereby effecting a white, brightappearance to the paper sheet when added to the stock furnish.Representative optical brighteners include, but are not limited toazoles, biphenyls, coumarins, furans, stilbenes, ionic brighteners,including anionic, cationic, and anionic (neutral) compounds, such asthe Eccobrite™ and Eccowhite™ compounds available from Eastern Color &Chemical Co. (Providence, R.I.); naphthalimides; pyrazenes; substituted(e.g., sulfonated) stilbenes, such as the Leucophor™ range of opticalbrighteners available from the Clariant Corporation (Muttenz,Switzerland), and Tinopal™ from Ciba Specialty Chemicals (Basel,Switzerland); salts of such compounds including but not limited toalkali metal salts, alkaline earth metal salts, transition metal salts,organic salts and ammonium salts of such brightening agents; andcombinations of one or more of the foregoing agents.

In one embodiment, the optical brighteners are selected from the groupincluding disulfonated, tetrasulfonated, and hexasulfonatedstilbene-based OBAs, and combinations thereof.

In one embodiment, an effective dosage of divalent metal salt,complexing agent, and optical brightener is the amount necessary toachieve the desired brightness and whiteness yet maintain good ink andprinting properties.

The amount of optical brightening agent is not particularly limited solong as the desirable whiteness and/or brightness is obtained, which iseasily determined by one of ordinary skill in the papermaking art. Whenused in a sizing composition, the optical brighteners may be added inany amount ranging from 10 to 100 pounds per 100 pounds of sizing agent(e.g., ethylated starch). This range includes all values and subrangestherebetween, including 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65,70, 75, 80, 85, 90, 95 and 100 pounds. In another embodiment, theoptical brightening agent may be added in amounts ranging from about0.005 to about 4 weight percent based on the weight of the paperproduct, such as a recording sheet. This range includes all values andsubranges therebetween, including about 0.005, 0.006, 0.007, 0.008,0.009, 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09, 0.1, 0.2,0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1, 2, 3, and 4 weight percent basedon the weight of the paper product.

For example, the composition can be added to bleached pulp or paperproduct at any point in the paper manufacturing process. Some examplesof addition points include, but are not limited to (a) to the pulpslurry in the latency chest; (b) to the pulp during or after thebleaching stage in a storage, blending or transfer chest; (c) addingEDTA or DTPA before the final debleaching stage where the pH is alkaline(and upon bleaching by the final D stage, the pH will drop which willimmobilize the complexing agent inside or upon the pulp fiber); (d) topulp after bleaching, washing and dewatering followed by cylinder orflash drying; (e) before or after the cleaners; (f) before or after thefan pump to the paper machine headbox; (g) to the paper machine whitewater; (h) sprayed or showered onto the moving wet web after head boxforming but before wet press; (i) to the silo or save all; (j) in thepress section using, for example, a size press, coater or spray bar; (k)in the drying section using, for example, a size press, coater or spraybar; (l) on the calender using a wafer box; (m) on paper in anoff-machine coater or size press; and/or (n) in the curl control unit.Combinations are possible.

The precise location where the composition is added will depend on thespecific equipment involved, the exact process conditions being used andthe like. In some cases, one or more of the divalent metal salt,complexing agent, and optical brightening agent may be added at one ormore locations for optimal effectiveness.

Application can be by any means conventionally used in papermakingprocesses, including by “split-feeding” whereby one or more of thedivalent metal salt, complexing agent, and optical brightening agentis/are applied at one point in the papermaking process, for example onpulp or a wet sheet (before the dryers) and the remaining portion of oneor more of the divalent metal salt, complexing agent, and opticalbrightening agent is added at a subsequent point, for example in thesize press.

In one embodiment, the complexing agent and/or optical brightener can beadded to a bleached pulp or paper product before, after orsimultaneously with the divalent metal salt. The optical brightenerand/or complexing agent may also be formulated with the divalent metalsalt.

In another embodiment, the composition may be mixed with a surfacesizing solution and applied in the size press.

In one embodiment, the composition is applied to a paper substrate toproduce a recording sheet. The paper substrate suitably comprises aplurality of cellulosic fibers. The type of cellulosic fiber is notcritical, and any such fiber known or suitable for use in paper makingcan be used. For example, the substrate can made from pulp fibersderived from hardwood trees, softwood trees, or a combination ofhardwood and softwood trees. The fibers may be prepared for use in apapermaking furnish by one or more known or suitable digestion,refining, and/or bleaching operations such as, for example, knownmechanical, thermomechanical, chemical and/or semichemical pulpingand/or other well known pulping processes. The term, “hardwood pulps” asmay be used herein include fibrous pulp derived from the woody substanceof deciduous trees (angiosperms) such as birch, oak, beech, maple, andeucalyptus. The term, “softwood pulps” as may be used herein includefibrous pulps derived from the woody substance of coniferous trees(gymnosperms) such as varieties of fir, spruce, and pine, as for exampleloblolly pine, slash pine, Colorado spruce, balsam fir and Douglas fir.In some embodiments, at least a portion of the pulp fibers may beprovided from non-woody herbaceous plants including, but not limited to,kenaf, hemp, jute, flax, sisal, or abaca, although legal restrictionsand other considerations may make the utilization of hemp and otherfiber sources impractical or impossible. Either bleached or unbleachedpulp fiber may be utilized. Recycled pulp fibers are also suitable foruse.

The paper substrate may suitably contain from 1 to 99 wt % of cellulosicfibers based upon the total weight of the substrate. In one embodiment,the paper substrate may contain from 5 to 95 wt % of cellulosic fibersbased upon the total weight of the substrate. These ranges include anyand all values and subranges therebetween, for example, 1, 5, 10, 15,20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95 and 99 wt%.

The paper substrate may optionally contain from 1 to 100 wt % cellulosicfibers originating from softwood species based upon the total amount ofcellulosic fibers in the paper substrate. In one embodiment, the papersubstrate may contain 10 to 60 wt % cellulosic fibers originating fromsoftwood species based upon the total amount of cellulosic fibers in thepaper substrate. These ranges include 1, 2, 5, 10, 15, 20, 25, 30, 35,40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95, and 100 wt % and any andall ranges and subranges therein, based upon the total amount ofcellulosic fibers in the paper substrate.

In one embodiment, the paper substrate may alternatively oroverlappingly contain from 0.01 to 99 wt % fibers from softwood species,based on the total weight of the paper substrate. In another embodiment,the paper substrate may contain from 10 to 60 wt % fibers from softwoodspecies based upon the total weight of the paper substrate. These rangesinclude any and all values and subranges therein. For example, the papersubstrate may contain not more than 0.01, 0.05, 0.1, 0.2, 0.5, 1, 2, 3,4, 5, 6, 7, 8, 9, 10, 12, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65,70, 75, 80, 85, 90, 95 and 99 wt % softwood based upon the total weightof the paper substrate.

All or part of the softwood fibers may optionally originate fromsoftwood species having a Canadian Standard Freeness (CSF) of from 300to 750. In one embodiment, the paper substrate contains fibers from asoftwood species having a CSF from 400 to 550. These ranges include anyand all values and subranges therebetween, for example, 300, 310, 320,330, 340, 350, 360, 370, 380, 390, 400, 410, 420, 430, 440, 450, 460,470, 480, 490, 500, 510, 520, 530, 540, 550, 560, 570, 580, 590, 600,610, 620, 630, 640, 650, 660, 670, 680, 690, 700, 710, 720, 730, 740,and 750 CSF. Canadian Standard Freeness is as measured by TAPPI T-227standard test.

The paper substrate may optionally contain from 1 to 100 wt % cellulosicfibers originating from hardwood species based upon the total amount ofcellulosic fibers in the paper substrate. In one embodiment, the papersubstrate may contain from 30 to 90 wt % cellulosic fibers originatingfrom hardwood species, based upon the total amount of cellulosic fibersin the paper substrate. These ranges include 1, 2, 5, 10, 15, 20, 25,30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95, and 100 wt %,and any and all values and subranges therein, based upon the totalamount of cellulosic fibers in the paper substrate.

In one embodiment, the paper substrate may alternatively oroverlappingly contain from 0.01 to 99 wt % fibers from hardwood species,based upon the total weight of the paper substrate. In anotherembodiment, the paper substrate may alternatively or overlappinglycontain from 60 to 90 wt % fibers from hardwood species, based upon thetotal weight of the paper substrate. These ranges include any and allvalues and subranges therebetween, including not more than 0.01, 0.05,0.1, 0.2, 0.5, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 12, 15, 20, 25, 30, 35,40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95, 99 and 99 wt %, basedupon the total weight of the paper substrate.

All or part of the hardwood fibers may optionally originate fromhardwood species having a Canadian Standard Freeness of from 300 to 750.In one embodiment, the paper substrate may contain fibers from hardwoodspecies having CSF values of from 400 to 550. These ranges include 300,310, 320, 330, 340, 350, 360, 370, 380, 390, 400, 410, 420, 430, 440,450, 460, 470, 480, 490, 500, 510, 520, 530, 540, 550, 560, 570, 580,590, 600, 610, 620, 630, 640, 650, 660, 670, 680, 690, 700, 710, 720,730, 740, and 750 CSF, and any and all ranges and subranges therein.

The paper substrate may optionally contain less refined fibers, forexample, less refined softwood fibers, less refined hardwood, or both.Combinations of less refined and more refined fibers are possible. Inone embodiment, the paper substrate contains fibers that are at least 2%less refined than that of fibers used in conventional paper substrates.This range includes all values and subranges therebetween, including atleast 2, 5, 10, 15, and 20%. For example, if a conventional papercontains fibers, softwood and/or hardwood, having a Canadian StandardFreeness of 350, then, in one embodiment, the paper substrate maycontain fibers having a CSF of 385 (i.e. refined 10% less thanconventional) and still perform similar, if not better, than theconventional paper. Nonlimiting examples of some performance qualitiesof the paper substrate are discussed below. Examples of some reductionsin refining of hardwood and/or softwood fibers include, but are notlimited to: 1) from 350 to at least 385 CSF; 2) from 350 to at least 400CSF; 3) from 400 to at least 450 CSF; and 4) from 450 to at least 500CSF. In some embodiments, the reduction in fiber refinement may be atleast 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19,20, and 25% reduction in refining compared to those fibers inconventional paper substrates.

When the paper substrate contains both hardwood fibers and softwoodfibers, the hardwood/softwood fiber weight ratio may optionally rangefrom 0.001 to 1000. In one embodiment, the hardwood/softwood ratio mayrange from 90/10 to 30/60. These ranges include all values and subrangestherebetween, including 0.001, 0.002, 0.005, 0.01, 0.02, 0.05, 0.1, 0.2,0.5, 1, 2, 5, 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75,80, 85, 90, 95, 100, 200, 300, 400, 500, 600, 700, 800, 900, and 1000.

The softwood fibers, hardwood fibers, or both may be optionally modifiedby physical and/or chemical processes. Examples of physical processesinclude, but are not limited to, electromagnetic and mechanicalprocesses. Examples of electrical modifications include, but are notlimited to, processes involving contacting the fibers with anelectromagnetic energy source such as light and/or electrical current.Examples of mechanical modifications include, but are not limited to,processes involving contacting an inanimate object with the fibers.Examples of such inanimate objects include those with sharp and/or dulledges. Such processes also involve, for example, cutting, kneading,pounding, impaling, and the like, and combinations thereof.

Nonlimiting examples of chemical modifications include conventionalchemical fiber processes such as crosslinking and/or precipitation ofcomplexes thereon. Other examples of suitable modifications of fibersinclude those found in U.S. Pat. Nos. 6,592,717, 6,592,712, 6,582,557,6,579,415, 6,579,414, 6,506,282, 6,471,824, 6,361,651, 6,146,494,H1,704, 5,731,080, 5,698,688, 5,698,074, 5,667,637, 5,662,773,5,531,728, 5,443,899, 5,360,420, 5,266,250, 5,209,953, 5,160,789,5,049,235, 4,986,882, 4,496,427, 4,431,481, 4,174,417, 4,166,894,4,075,136, and 4,022,965, the entire contents of each of which arehereby incorporated, independently, by reference. Still other examplesof suitable modifications of fibers may be found in U.S. ApplicationNos. 60/654,712, filed Feb. 19, 2005, and Ser. No. 11/358,543, filedFeb. 21, 2006, which may include the further addition of opticalbrighteners (i.e. OBAs) as discussed therein, the entire contents ofeach of which are hereby incorporated, independently, by reference.

The paper substrate may optionally include “fines.” “Fines” fibers aretypically those fibers with average lengths of not more than about 100μm. Sources of “fines” may be found in SaveAll fibers, recirculatedstreams, reject streams, waste fiber streams, and combinations thereof.The amount of “fines” present in the paper substrate can be modified,for example, by tailoring the rate at which streams are added to thepaper making process. In one embodiment, the average lengths of thefines are not more than about 5, 10, 15, 20, 25, 30, 35, 40, 45, 50, 55,60, 65, 70, 75, 80, 85, 90, 95, and 100 μm, including any and all rangesand subranges therein.

If used, the “fines” fibers may be present in the paper substratetogether with hardwood fibers, softwood fibers, or both hardwood andsoftwood fibers.

The paper substrate may optionally contain from 0.01 to 100 wt % fines,based on the total weight of the paper substrate. In one embodiment, thepaper substrate may contain from 0.01 to 50 wt % fines, based upon thetotal weight of the substrate. These ranges include all values andsubranges therebetween, including not more than 0.01, 0.05, 0.1, 0.2,0.5, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 12, 15, 20, 25, 30, 35, 40, 45, 50,55, 60, 65, 70, 75, 80, 85, 90, 95 and 100 wt % fines, based upon thetotal weight of the paper substrate.

In one embodiment, the paper substrate may alternatively oroverlappingly contain from 0.01 to 100 wt % fines, based upon the totalweight of the fibers in the paper substrate. This range includes allvalues and subranges therebetween, including not more than 0.01, 0.05,0.1, 0.2, 0.5, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 12, 15, 20, 25, 30, 35,40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95 and 100 wt % fines, basedupon the total weight of the fibers in by the paper substrate.

If desired, the recording sheet may contain at least one sizing agent inaddition to the composition. The sizing agent is not particularlylimited, and any conventional papermaking sizing agent may be used. Thesizing agent may be nonreactive, reactive, or a combination ofnonreactive and reactive. The sizing agent may, optionally and ifdesired, impart a moisture or water-resistance in varying degrees to thepaper substrate. Non-limiting examples of sizing agents can be found inthe “Handbook for Pulp and Paper Technologists” by G. A. Smook (1992),Angus Wilde Publications, which is hereby incorporated, in its entirety,by reference. Preferably, the sizing agent is a surface sizing agent.Preferable examples of sizing agents are starch, alkyl ketene dimer(AKD), alkenyl ketene dimer (ALKD), alkenyl succinic anhydride (ASA),ASA/ALKD, styrene acrylic emulsion (SAE) polyvinyl alcohol (PVOH),polyvinylamine, alginate, carboxymethyl cellulose, etc. However, anysizing agent may be used. See, for example, the sizing agents disclosedin U.S. Pat. No. 6,207,258, the entire contents of which are herebyincorporated by reference.

Many nonreactive sizing agents are known in the art. Examples include,without limitation, BASOPLAST® 335D nonreactive polymeric surface sizeemulsion from BASF Corporation (Mt. Olive, N.J.), FLEXBOND® 325 emulsionof a copolymer of vinyl acetate and butyl acrylate from Air Products andChemicals, Inc. (Trexlertown, Pa.), and PENTAPRINT® nonreactive sizingagents (disclosed for example in Published International PatentApplication Publication No. WO 97/45590, published Dec. 4, 1997,corresponding to U.S. patent application Ser. No. 08/861,925, filed May22, 1997, the entire contents of which are hereby incorporated byreference) from Hercules Incorporated (Wilmington, Del.), to name a few.

For papermaking carried out under alkaline pH manufacturing conditions,sizing agents based on alkyl ketene dimers (AKDs) or alkenyl ketenedimers (ALKDs) or multimers and alkenyl succinic anhydride (ASA) sizingagents may be suitably used. Combinations of these and other sizingagents may also be employed.

Ketene dimers used as sizing agents for papermaking are well known.AKDs, containing one β-lactone ring, are typically prepared by thedimerization of alkyl ketenes made from two fatty acid chlorides.Commercial alkyl ketene dimer sizing agents are often prepared frompalmitic and/or stearic fatty acids, e.g. Hercon® and Aquapel® sizingagents (both from Hercules Incorporated).

Alkenyl ketene dimer sizing agents are also commercially available, e.g.Precis® sizing agents (Hercules Incorporated).

U.S. Pat. No. 4,017,431, the entire contents of which are herebyincorporated by reference, provides a nonlimiting exemplary disclosureof AKD sizing agents with wax blends and water soluble cationic resins.

Ketene multimers containing more than one β-lactone ring may also beemployed as sizing agents.

Sizing agents prepared from a mixture of mono- and dicarboxylic acids,have been disclosed as sizing agents for paper in Japanese Kokai Nos.168991/89 and 168992/89.

European patent application Publication No. 0 629 741 A1 discloses alkylketene dimer and multimer mixtures as sizing agents in paper used inhigh speed converting and reprographic machines. The alkyl ketenemultimers are made from the reaction of a molar excess of monocarboxylicacid, typically a fatty acid, with a dicarboxylic acid. These multimercompounds are solids at 25° C.

European patent application Publication No. 0 666 368 A2 and Bottorff etal. in U.S. Pat. No. 5,685,815, the entire contents of which are herebyincorporated by reference, disclose paper for high speed or reprographicoperations that is internally sized with an alkyl or alkenyl ketenedimer and/or multimer sizing agent. The preferred 2-oxetanone multimersare prepared with fatty acid to diacid ratios ranging from 1:1 to 3.5:1.

Commercial ASA-based sizing agents are dispersions or emulsions ofmaterials that may be prepared by the reaction of maleic anhydride withan olefin (C₁₄-C₁₈).

Examples of hydrophobic acid anhydrides useful as sizing agents forpaper include:

(i) rosin anhydride (see U.S. Pat. No. 3,582,464, for example, theentire contents of which are hereby incorporated by reference);

(ii) anhydrides having the structure (I):

where each R is the same or a different hydrocarbon radical; and

(iii) cyclic dicarboxylic acid anhydrides, such as those having thestructure (II):

where R′ represents a dimethylene or trimethylene radical and where R″is a hydrocarbon radical.

Some examples of anhydrides of formula (I) include myristoyl anhydride;palmitoyl anhydride; olcoyl anhydride; and stearoyl anhydride.

Examples of substituted cyclic dicarboxylic acid anhydrides fallingwithin the above formula (II) include substituted succinic, glutaricanhydrides, i- and n-octadecenyl succinic acid anhydride; i- andn-hexadecenyl succinic acid anhydride; i- and n-tetradecenyl succinicacid anhydride, dodecyl succinic acid anhydride; decenyl succinic acidanhydride; ectenyl succinic acid anhydride; and heptyl glutaric acidanhydride.

Other examples of nonreactive sizing agents include a polymer emulsion,a cationic polymer emulsion, an amphoteric polymer emulsion, polymeremulsion wherein at least one monomer is selected from the groupincluding styrene, α-methylstyrene, acrylate with an ester substituentwith 1 to 13 carbon atoms, methacrylate having an ester substituent with1 to 13 carbon atoms, acrylonitrile, methacrylonitrile, vinyl acetate,ethylene and butadiene; and optionally including acrylic acid,methacrylic acid, maleic anhydride, esters of maleic anhydride ormixtures thereof, with an acid number less than about 80, and mixturesthereof.

If desired, the polymer emulsion may stabilized by a stabilizerpredominantly including degraded starch, such as that disclosed, forexample, in U.S. Pat. Nos. 4,835,212, 4,855,343, and 5,358,998, theentire contents of each of which are hereby incorporated by reference.If desired, a polymer emulsion may be used in which the polymer has aglass transition temperature of about −15° C. to about 50° C.

For traditional acid pH papermaking conditions, nonreactive sizingagents in the form of dispersed rosin sizing agents may be suitablyused. Dispersed rosin sizing agents are well known. Nonlimiting examplesof rosin sizing agents are disclosed in, for example, U.S. Pat. Nos.3,966,654 and 4,263,182, the entire contents of each of which are herebyincorporated by reference.

The rosin may be any modified or unmodified, dispersible or emulsifiablerosin suitable for sizing paper, including unfortified rosin, fortifiedrosin and extended rosin, as well as rosin esters, and mixtures andblends thereof. As used herein, the term “rosin” means any of theseforms of dispersed rosin useful in a sizing agent.

The rosin in dispersed form is not particularly limited, and any of thecommercially available types of rosin, such as wood rosin, gum rosin,tall oil rosin, and mixtures of any two or more, in their crude orrefined state, may be used. In one embodiment, tall oil rosin and gumrosin are used. Partially hydrogenated rosins and polymerized rosins, aswell as rosins that have been treated to inhibit crystallization, suchas by heat treatment or reaction with formaldehyde, may also beemployed.

The fortified rosin is not particularly limited. One example of such arosin includes the adduct reaction product of rosin and an acidiccompound containing the

group and is derived by reacting rosin and the acidic compound atelevated temperatures of from about 150° C. to about 210° C.

The amount of acidic compound employed will be that amount which willprovide fortified rosin containing from about 1% to about 16% by weightof adducted acidic compound based on the weight of the fortified rosin.Methods of preparing fortified rosin are well known to those skilled inthe art. See, for example, the methods disclosed and described in U.S.Pat. Nos. 2,628,918 and 2,684,300, the entire contents of each of whichare hereby incorporated by reference.

Examples of acidic compounds containing the

group that can be used to prepare the fortified rosin include theα-β-unsaturated organic acids and their available anhydrides, specificexamples of which include fumaric acid, maleic acid, acrylic acid,maleic anhydride, itaconic acid, itaconic anhydride, citraconic acid andcitraconic anhydride. Mixtures of acids can be used to prepare thefortified rosin if desired.

Thus, for example, a mixture of the acrylic acid adduct of rosin and thefumaric acid adduct can be used to prepare a dispersed rosin sizingagent. Also, fortified rosin that has been substantially completelyhydrogenated after adduct formation can be used.

Rosin esters may also be used in the dispersed rosin sizing agents.Suitable exemplary rosin esters may be rosin esterified as disclosed inU.S. Pat. No. 4,540,635 (Ronge et al.) or U.S. Pat. No. 5,201,944(Nakata et al.), the entire contents of each of which are herebyincorporated by reference.

The unfortified or fortified rosin or rosin esters can be extended ifdesired by known extenders such as waxes (particularly paraffin wax andmicrocrystalline wax); hydrocarbon resins including those derived frompetroleum hydrocarbons and terpenes; and the like. This may be suitablyaccomplished by melt blending or solution blending with the rosin orfortified rosin from about 10% to about 100% by weight, based on theweight of rosin or fortified rosin, of the extender.

Blends of fortified rosin and unfortified rosin; blends of fortifiedrosin, unfortified rosin, rosin esters and rosin extender can be used.Blends of fortified and unfortified rosin may include, for example,about 25% to 95% fortified rosin and about 75% to 5% unfortified rosin.Blends of fortified rosin, unfortified rosin, and rosin extender mayinclude, for example, about 5% to 45% fortified rosin, 0 to 50% rosin,and about 5% to 90% rosin extender.

Hydrophobic organic isocyanates, e.g., alkylated isocyanates, may alsobe used as sizing agents.

Other conventional paper sizing agents include alkyl carbamoylchlorides, alkylated melamines such as stearylated melamines, andstyrene acrylates.

Mixtures of sizing agents are possible.

An external sizing agent or both internal and surface sizing agents maybe used. Either or both may contain the divalent metal salt, the opticalbrightening agent, and the complexing agent. When both internal andexternal sizing agents are present, they may be present in any weightratio and may be the same and/or different. In one embodiment, theweight ratio of surface sizing agent to internal sizing agent is from50/50 to 100/0, more preferably from 75/25 to 100/0 surface/internalsizing agent. This range includes 50/50, 55/45, 60/40, 65/35, 70/30,75/25, 80/20, 85/15, 90/10, 95/5 and 100/0, including any and all rangesand subranges therein. A preferred example of an internal sizing agentis alkenyl succinic anhydride (ASA).

When starch is used as a sizing agent, starch may be modified orunmodified. Examples of starch may be found in the “Handbook for Pulpand Paper Technologists” by G. A. Smook (1992), Angus WildePublications, mentioned above. Preferable examples of modified starchesinclude, for example, oxidized, cationic, ethylated, hydroethoxylated,etc. In addition, the starch may come from any source, preferably potatoand/or corn. Most preferably, the starch source is corn.

In one embodiment, a mixture comprising calcium chloride, complexingagent, optical brightening agent, and one or more starches is in contactwith at least one surface of the substrate. Illustrative of usefulstarches include naturally occurring carbohydrates synthesized in corn,tapioca, potato and other plants by polymerization of dextrose units.All such starches and modified forms thereof such as starch acetates,starch esters, starch ethers, starch phosphates, starch xanthates,anionic starches, cationic starches, oxidized starches, and the likewhich can be derived by reacting the starch with a suitable chemical orenzymatic reagent can be used. If desired, starches may be prepared byknown techniques or obtained from commercial sources. For example, oneexample of a commercial starches include Ethylex 2035 from A.E. Staley,PG-280 from Penford Products, oxidized corn starches from ADM, Cargill,and Raisio, and enzyme converted starches such as Amyzet 150 fromAmylum.

Modified starches may be used. Non-limiting examples of a type ofmodified starches include cationic modified chemically modified starchessuch as ethylated starches, oxidized starches, and AP and enzymeconverted Pearl starches. Most preferred are chemically modifiedstarches such as ethylated starches, oxidized starches, and AP andenzyme converted Pearl starches.

In one embodiment, a water soluble metal salt, for example, calciumchloride, and Ethylex 2035 starch together with a complexing agent andan optical brightening agent are used in a sizing formulation applied toboth sides of a sheet of paper, and an improved dry time of the sheet isobtained when the weight ratio of the calcium chloride to the starch isequal to or greater than about 0.5 to about 20%. This range includes allvalues and subranges therebetween, including 0.5, 0.6, 0.7, 0.8, 0.9, 1,1.5, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, and20%, and any combination thereof. In one embodiment, the weight ratio ofthe calcium chloride to the starch may range from about 0.5 to about18%. In another embodiment, the weight ratio may range from about 0.75to about 17%. In another embodiment, the weight ratio may range fromabout 1% to about 16%. The weight ratios of the calcium chloride to thestarch may be one-half of those stated if the starch/salt mixture isonly applied to one side of the paper, and starch without salt isapplied to the other side. In this case, the improved print propertieswould only be expected on the side of the paper containing the salt.

The amount of divalent water soluble metal salt and one or more starchesin and/or on the substrate may vary widely, and any conventional amountcan be used.

When polyvinyl alcohol is used as a sizing agent, it may have any %hydrolysis. Preferable polyvinyl alcohols are those having a %hydrolysis ranging from 100% to 75%. The % hydrolysis of the polyvinylalcohol may be 75, 76, 78, 80, 82, 84, 85, 86, 88, 90, 92, 94, 95, 96,98, and 100% hydrolysis, including any and all ranges and subrangestherein.

The paper substrate may contain PVOH at any wt %. Preferably, when PVOHis present, it is present at an amount from 0.001 wt % to 100 wt % basedon the total weight of sizing agent contained in and/or on thesubstrate. This range includes 0.001, 0.002, 0.005, 0.006, 0.008, 0.01,0.02, 0.03, 0.04, 0.05, 0.1, 0.2, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1, 2, 4,5, 6, 8, 10, 12, 14, 15, 16, 18, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65,70, 75, 80, 85, 90, 95, and 100 wt % based on the total weight of sizingagent in the substrate, including any and all ranges and subrangestherein.

The sizing agent may also include one or more optional additives such asbinders, pigments, thickeners, defoamers, surfactants, slip agents,dispersants, optical brighteners, dyes, and preservatives, which arewell-known. Examples of pigments include, but are not limited to, clay,calcium carbonate, calcium sulfate hemihydrate, and calcium sulfatedehydrate, chalk, GCC, PCC, and the like. A preferable pigment iscalcium carbonate with the preferred form being precipitated calciumcarbonate. Examples of binders include, but are not limited to,polyvinyl alcohol, Amres (a Kymene type), Bayer Parez, polychlorideemulsion, modified starch such as hydroxyethyl starch, starch,polyacrylamide, modified polyacrylamide, polyol, polyol carbonyl adduct,ethanedial/polyol condensate, polyamide, epichlorohydrin, glyoxal,glyoxal urea, ethanedial, aliphatic polyisocyanate, isocyanate, 1,6hexamethylene diisocyanate, diisocyanate, polyisocyanate, polyester,polyester resin, polyacrylate, polyacrylate resin, acrylate, andmethacrylate. Other optional additives include, but are not limited tosilicas such as colloids and/or sols. Examples of silicas include, butare not limited to, sodium silicate and/or borosilicates. Otheradditives which may be used include one or more solvents such as, forexample, water. Combinations of additives are possible.

It may be advantageous that a majority of the total amount of sizingagent is located at or near the outside surface or surfaces (in the caseof the sizing applied to both surfaces) of the paper substrate. In oneembodiment, the paper substrate contains the sizing agent such that they(the substrate and the sizing agent) cooperate to form an I-beamstructure. I-beam structures are discussed, for example, in U.S. PatentPublication Nos. 2004/0065423, published Apr. 8, 2004, and 2008/0035292filed Jan. 7, 2007, as well as in the U.S. Provisional Application filedMar. 31, 2008, and having Application Ser. No. 61/040,806, the entirecontents of each of which are hereby incorporated by reference. In thisregard, it is not required that the sizing agent interpenetrate with thecellulosic fibers of the substrate. However, if the sizing or coatinglayer and the cellulose fibers interpenetrate, it will create a papersubstrate having an interpenetration layer, which is within the ambit ofthe present invention.

In one embodiment, the interpenetration layer of the paper substrate maydefine a region in which at least the sizing solution penetrates intoand is among the cellulose fibers. The interpenetration layer may befrom 1 to 99% of the entire cross section of at least a portion of thepaper substrate, including 1, 2, 5, 10, 15, 20, 25, 30, 35, 40, 45, 50,55, 60, 65, 70, 75, 80, 85, 90, 95, and 99% of the paper substrate,including any and all ranges and subranges therein. Such an embodimentmay be made, for example, when a sizing solution is added to thecellulose fibers prior to a coating method and may be combined with asubsequent coating method if required. Addition points may be at thesize press, for example.

In one embodiment, the cross-sectional thickness of the interpenetrationlayer may be minimized. Alternatively, or additionally, theconcentration of the sizing agent preferably increases as one moves (inthe z-direction normal to the plane of the substrate) from the interiorportion towards the surface of the paper substrate. Therefore, theamount of sizing agent present towards the top and/or bottom outersurfaces of the substrate may be greater than the amount of sizing agentpresent towards the inner middle of paper substrate. Alternatively, amajority percentage of the sizing agent may preferably be located at adistance from the outside surface of the substrate that is equal to orless than 25%, more preferably 10%, of the total thickness of thesubstrate. This aspect may also be known as the Q_(total), which ismeasured by known methodologies outlined, for example, in U.S. PatentPublication No. 2008/0035292, published Feb. 14, 2008, the entirecontents of which are hereby incorporated by reference. If Q_(total) isequal to 0.5, then the sizing agent is approximately evenly distributedthroughout the paper substrate. If Q_(total) is greater than 0.5, thenthere is more sizing agent towards the central portion (measured by thez-direction normal to the plane of the substrate) of the paper substratethan towards the paper substrate's surface or surfaces. If Q_(total) isless than 0.5, then there is less sizing agent towards the centralportion of the paper substrate than towards the paper substrate'ssurface or surfaces. In light of the above, the paper substratepreferably has a Q_(total) that is less than 0.5, preferably less than0.4, more preferably less than 0.3, most preferably less than 0.25.Accordingly the Q_(total) of the paper substrate may be from 0 to lessthan 0.5. This range includes 0, 0.001, 0.002, 0.005, 0.01, 0.02, 0.05,0.1, 0.15, 0.2, 0.25, 0.3, 0.35, 0.4, 0.45, and 0.49, including any andall ranges and subranges therein.

As noted above, the determination of Q may be suitably carried outaccording to the procedures in U.S. Patent Publication 2008/0035292,published Feb. 14, 2008.

In essence, Q is a measurement of the amount of the starch as oneprogresses from the outside edges towards the middle of the sheet from across section view. It is understood herein that the Q may be any Q suchthat it represents an enhanced capacity to have starch towards theoutside surfaces of the cross section of the sheet and Q may be selected(using any test) such that any one or more of the above andbelow-mentioned characteristics of the paper substrate are provided(e.g. Internal Bond, Hygroexpansivity, IGT Pick, and/or IGT VPPdelamination, etc).

Other methods are available for measuring the equivalent of Q. In oneembodiment, any Q measurement, or a similar method of measuring theratio of the amount of sizing agent containing the composition towardsthe core of the substrate compared to the amount of sizing agent towardsthe outside surface or surfaces of the substrate is acceptable. In oneembodiment, this ratio is such that as much sizing agent as possible islocated towards the outside surfaces of the substrate, therebyminimizing the interpenetration zone and/or minimizing the amount ofstarch located in the interpenetration layer, is achieved. It is alsopossible that the distribution of sizing agent occurs even at very highlevel of sizing agent loadings, preferably external sizing agentloadings, within and/or onto the substrate. Thus, in the case that anI-beam structure is formed, it is desirable to control the amount ofsizing agent located within the interpenetration layer as more and moreexternal sizing agent is loaded thereon its surface by either minimizingthe concentration of the sizing agent in this interpenetration layer orby reducing the thickness of the interpenetration layer itself. In oneembodiment, the characteristics of the recording sheet and/or papersubstrate are those that can be achieved by such control of the sizingagent. While this controlled loading of the sizing agent can occur inany manner, it is preferable that the sizing agent is loaded or appliedvia a size press.

The recording sheet may be made by contacting the composition,containing a sizing agent with the cellulose fibers of the papersubstrate. The contacting may occur at acceptable concentration levelsof the sizing agent and/or other additives.

The recording sheet may be made by contacting the substrate with aninternal and/or surface sizing solution or formulation containing thecomposition according to the present invention and additionally at leastone sizing agent. The contacting may occur anytime in the papermakingprocess including, but not limited to the wet end, head box, size press,water box, and/or coater. Further addition points include machine chest,stuff box, and suction of the fan pump. The cellulose fibers, sizingagent, and/or optional components may be contacted serially,consecutively, and/or simultaneously in any combination with each other.Most preferably, the paper substrate is contacted with the size pressformulation at the size press.

The paper substrate may be passed through a size press, where any sizingmeans commonly known in the art of papermaking is acceptable. The sizepress, for example, may be a puddle mode size press (e.g. inclined,vertical, horizontal) or metered size press (e.g. blade metered, rodmetered). Preferably, the size press is a metered size press.

To prepare the size press formulation, one or more divalent watersoluble metal salts may be admixed with one or more sizing agents forexample, starches, and one or more optional additives can be dissolvedor dispersed in an appropriate liquid medium, preferably water, and canbe applied to the substrate.

For example, the size press formulation can be applied with conventionalsize press equipment having vertical, horizontal or inclined size pressconfigurations conventional used in paper preparation as for example theSymsizer (Valmet) type equipment, a KRK size press (Kumagai Riki KogyoCo., Ltd., Nerima, Tokyo, Japan) by dip coating. The KRK size press is alab size press that simulates a commercial size press. This size pressis normally sheet fed, whereas a commercial size press typically employsa continuous web.

In one embodiment, the sizing agent is applied in an amount such suchthat a dry pickup of 30 to 150 lbs of starch/ton of paper at 12-50%solids for the size press formulation. Here, lbs/ton is calculated on apaper having a basis weight equal to 75 gsm.

The aforementioned range of starch includes all values and subrangestherebetween, including 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85,90, 95, 100, 105, 110, 115, 120, 125, 130, 135, 140, 145, and 150lbs/ton. Here, lbs/ton is calculated on a paper having a basis weightequal to 75 gsm.

It should be readily apparent that the amounts in lbs/ton and moles/tonmay vary in a known manner according to the basis weight of the paper,and the invention is not limited to only paper having a basis weight of75 gsm.

In one embodiment, wherein an I-beam structure is formed, in whichcalcium chloride is used as the water soluble metal salt, and in which asizing agent is present on both sides of a sheet of paper, the amountranges from about 2 to about 8 lbs of CaCl₂/ton of paper on a paperhaving a basis weight equal to 75 gsm. This range includes all valuesand subranges therebetween, including about 2, 3, 4, 5, 6, 7, and 8 lbsof CaCl₂/ton of paper. This range is equal to a range from about 0.6 to8 lbs of CaCl₂/ton of paper on a paper having a basis weight equal to250 gsm. This range includes all values and subranges therebetween,including 0.6, 1, 2, 3, 4, 5, 6, 7, and 8 lbs of CaCl₂/ton of paper.

In one embodiment, the % solids in the size press formulation maysuitably range from at least 12-50%. This range includes all values andsubranges therebetween, including 12, 13, 14, 15, 16, 17, 18, 19, 20,21, 22, 23, 24, 25, 30, 35, 40, 45, and 50%.

In one embodiment, the dry pickup of the sizing agent may suitably rangefrom 0.25 to 6 gsm, which range includes all values and subrangestherebetween, for example, 0.25, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1,2, 3, 4, 5, and 6 gsm, and any combination thereof.

In one embodiment, the wet film thickness is adjusted to give properpickup. For example, in one embodiment, the wet film thickness maysuitably range from greater than zero to 40 mm. This range includes allvalues and subranges therebetween, including greater than zero, 1, 2, 3,4, 5, 6, 7, 8, 9, 10, 15, 16, 17, 18, 19, 20, 25, 30, 35, and 40microns. In one embodiment, the wet film thickness ranges from 10 to 30microns. In one embodiment, the wet film thickness ranges from 15 to 25microns.

In one embodiment, the amount of pigment at the size press (in thesizing formulation) may suitably range from 10 to 80 lbs/ton. This rangeincludes all values and subranges therebetween, including 10, 11, 12,13, 14, 15, 16, 17, 18, 19, 20, 22, 24, 26, 28, 30, 35, 40, 45, 50, 55,60, 65, 60, 75 and 80 lbs/ton. Here, lbs/ton is calculated using a basisweight of 20# bond paper (75 gsm).

In one embodiment, the temperature at the size press may suitably rangefrom 100-300° F. This range includes all values and subrangestherebetween, including 100, 110, 120, 130, 140, 150, 160, 170, 180,190, 200, 210, 220, 230, 240, 250, 260, 270, 280, 290, and 300° F.

In one embodiment, a rod-metered size press is used. In such anembodiment, a suitable rod volume may range from 0.000864 in²/in to0.001637 in²/in. This range includes all values and subrangestherebetween, including 0.000865, 0.00087, 0.0009, 0.0010, 0.0015, and0.001637 in²/in.

When the cellulosic fibers are contacted with the size press formulationat the size press, it is preferred that the viscosity of the sizingsolution is from 50 to 500 centipoise using a Brookfield Viscometer,number 2 spindle, at 100 rpm and 150° F. These ranges include all valuesand subranges therebetween, including 50, 55, 60, 65, 70, 75, 80, 85,90, 95, 100, 125, 150, 160, 170, 180, 190, 200, 210, 220, 230, 240, 250,260, 270, 280, 290, 300, 325, 350, 375, 400, 425, and 450 centipoise asmeasured using a Brookfield Viscometer, number 2 spindle, at 100 rpm and150° F., including any and all ranges and subranges therein. In oneembodiment, the viscosity ranges from 50 to 350 centipoise. In anotherembodiment, the viscosity ranges from 100 to 500 centipoise.

The paper substrate may be pressed in a press section containing one ormore nips. Any pressing means commonly known in the art of papermakingmay be utilized. The nips may be, but are not limited to, single felted,double felted, roll, and extended nip in the presses. When the sizingsolution containing the sizing agent is contacted with the fibers at thesize press to make the paper substrate, the effective nip pressure isnot particularly limited so long as integrity of the I-beam structure ismaintained. For example, the nip pressure may suitably range fromgreater than zero to 80 kN/m. This range includes all values andsubranges therebetween, including greater than zero, 1, 2, 3, 4, 5, 6,7, 8, 9, 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, 70, and 80 kN/m,including any and all ranges and subranges therein. In one embodiment,the nip pressure ranges from 30 to 80 kN/m.

The nip width is not particularly limited, and may suitably range fromgreater than zero to 40 mm. This range includes all values and subrangestherebetween, including greater than zero, 1, 2, 3, 4, 5, 6, 7, 8, 9,10, 15, 16, 17, 18, 19, 20, 25, 30, 35, and 40 mm. In one embodiment,the nip width ranges from 15 to 30 mm.

The rolls of the size press may have a P&J hardness, preferably any P&Jhardness. Since there are two rolls, a first roll may have a firsthardness, while a second roll may have a second hardness. The rollhardness may suitably range from 0 to 30 P&J hardness. This rangeincludes all values and subranges therebetween, including 0, 1, 2, 3, 4,5, 6, 7, 8, 9, 10, 15, 20, 25, and 30 P&J hardness. If two rolls areused, they may have the same or different hardnesses. The first hardnessand the second hardness may be equal and/or different from one another.As an example, the P&J of a first roll at the size press may have afirst hardness that independently ranges from 0 to 30 P&J hardness,while the second roll may have a second hardness that independentlyranges from 0 to 30 P&J hardness.

The paper substrate may be dried in a drying section. Any drying meanscommonly known in the art of papermaking may be utilized. The dryingsection may include and contain a drying can, cylinder drying, Condebeltdrying, IR, or other drying means and mechanisms known in the art. Thepaper substrate may be dried so as to contain any selected amount ofwater. Preferably, the substrate is dried to contain less than or equalto 10% water.

The paper substrate may be calendered by any commonly known calendaringmeans in the art of papermaking. More specifically, one could utilize,for example, wet stack calendering, dry stack calendering, steel nipcalendaring, hot soft calendaring or extended nip calendering, etc.

The paper substrate may be microfinished according to any processcommonly known in the art of papermaking. Microfinishing typicallyinvolves frictional processes to finish surfaces of the paper substrate.The paper substrate may be microfinished with or without a calenderingapplied thereto consecutively and/or simultaneously. Examples ofmicrofinishing processes can be found in U.S. Patent Publication No.2004/0123966 and references cited therein, as well as U.S. ProvisionalPatent Application No. 60/810,181 filed Jun. 2, 2006, which are allhereby, in their entirety, herein incorporated by reference.

In one embodiment, the paper substrate comprising the composition and asizing agent may be further coated by any conventional coating layerapplication means, including impregnation means. A preferred method ofapplying the coating layer is with an in-line coating process with oneor more stations. The coating stations may be any of known coating meanscommonly known in the art of papermaking including, for example, brush,rod, air knife, spray, curtain, blade, transfer roll, reverse roll,and/or cast coating means, as well as any combination of the same.

The further coated paper substrate may be dried in a drying section. Anydrying means commonly known in the art of papermaking and/or coatingsmay be utilized. The drying section may include and contain IR, airimpingement dryers and/or steam heated drying cans, or other dryingmeans and mechanisms known in the coating art.

The further coated substrate may be finished according to any finishingmeans commonly known in the art of papermaking. Examples of suchfinishing means, including one or more finishing stations, include glosscalendar, soft nip calendar, and/or extended nip calendar.

These paper substrate and/or recording sheet may be added to anyconventional papermaking processes, as well as converting processes,including abrading, sanding, slitting, scoring, perforating, sparking,calendaring, sheet finishing, converting, coating, laminating, printing,etc. In one embodiment, the conventional processes include thosetailored to produce paper substrates capable to be utilized as coatedand/or uncoated paper products, board, and/or substrates. These andother suitable processes may be found in textbooks such as the “Handbookfor Pulp and Paper Technologists” by G. A. Smook (1992), Angus WildePublications, which is hereby incorporated, in its entirety, byreference.

The recording sheet and/or paper substrate may also include one or moreoptional substances such as retention aids, binders, fillers,thickeners, and preservatives. Examples of fillers include, but are notlimited to, clay, calcium carbonate, calcium sulfate hemihydrate, andcalcium sulfate dehydrate, chalk, GCC, PCC, and the like. A preferablefiller is calcium carbonate with the preferred form being precipitatedcalcium carbonate. Examples of binders include, but are not limited to,polyvinyl alcohol, Amres (a Kymene type), Bayer Parez, polychlorideemulsion, modified starch such as hydroxyethyl starch, starch,polyacrylamide, modified polyacrylamide, polyol, polyol carbonyl adduct,ethanedial/polyol condensate, polyamide, epichlorohydrin, glyoxal,glyoxal urea, ethanedial, aliphatic polyisocyanate, isocyanate, 1,6hexamethylene diisocyanate, diisocyanate, polyisocyanate, polyester,polyester resin, polyacrylate, polyacrylate resin, acrylate, andmethacrylate. Other optional substances include, but are not limited tosilicas such as colloids and/or sols. Examples of silicas include, butare not limited to, sodium silicate and/or borosilicates. Anotherexample of optional substances are solvents including but not limited tosolvents such as water. Combinations of optional substances arepossible.

The recording sheet of the present invention may contain from 0.001 to20 wt % of the optional substances based on the total weight of thesubstrate, preferably from 0.01 to 10 wt %, most preferably 0.1 to 5.0wt %, of each of at least one of the optional substances. This rangeincludes 0.001, 0.002, 0.005, 0.006, 0.008, 0.01, 0.02, 0.03, 0.04,0.05, 0.1, 0.2, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1, 2, 4, 5, 6, 8, 10, 12,14, 15, 16, 18, and 20 wt % based on the total weight of the substrate,including any and all ranges and subranges therein.

Other conventional additives that may be present include, but are notlimited to, wet strength resins, internal sizes, dry strength resins,alum, fillers, pigments and dyes. The substrate may include bulkingagents such as expandable microspheres, pulp fibers, and/or diamidesalts.

The paper substrate or sizing agent may optionally contain a bulkingagent in any amount, if present, ranging from 0.25 to 50 dry lbs per tonof finished substrate, preferably from 5 to 20, dry lb per ton offinished product when such bulking means is an additive. This rangeincludes 0.25, 0.5, 0.75, 1.0, 2.0, 2.5, 3.0, 3.5, 4, 4.5, 5, 5.5, 6,6.5, 7, 7.5, 8, 8.5, 9, 9.5, 10, 11, 12, 13, 14, 15, 20, 25, 30, 35, 40,45, and 50 dry lb per ton of finished product, including any and allranges and subranges therein.

The bulking agent may be an expandable microsphere, composition, and/orparticle for bulking paper articles and substrates. However, any bulkingagent can be utilized, while the expandable microsphere, composition,particle and/or paper substrate of that follows is the preferred bulkingmeans. Other alternative bulking agents include, but are not limited to,surfactants, Reactopaque, pre-expanded spheres, BCTMP (bleachedchemi-thermomechanical pulp), microfinishing, and multiply constructionfor creating an I-beam effect in a paper or paper board substrate. Suchbulking agents may, when incorporated or applied to a paper substrate,provide adequate print quality, caliper, basis weight, etc in theabsence of harsh calendaring conditions (i.e. pressure at a single nipand/or less nips per calendaring means), yet produce a paper substratehaving the a single, a portion of, or combination of the physicalspecifications and performance characteristics mentioned herein.

In one embodiment, the paper substrate may contain from 0.001 to 10 wt%, preferably from 0.02 to 5 wt %, more preferably from 0.025 to 2 wt %,most preferably from 0.125 to 0.5 wt % of expandable microspheres basedon the total weight of the substrate.

Examples of expandable microspheres having bulking capacity are thosedescribed in U.S. Patent Application No. 60/660,703 filed Mar. 11, 2005,and U.S. patent application Ser. No. 11/374,239 filed Mar. 13, 2006,which are also hereby incorporated, in their entirety, by reference.Further examples include those found in U.S. Pat. No. 6,379,497, filedMay 19, 1999, and U.S. Patent Publication No. 2006/0102307, filed Jun.1, 2004, which are also hereby incorporated, in their entirety, byreference.

Some examples of bulking fibers include, but are not limited to,mechanical fibers such as ground wood pulp, BCTMP, and other mechanicaland/or semi-mechanical pulps. When such pulps are added, from 0.25 to 75wt %, preferably less than 60 wt % of total weight of the fibers usedmay be from such bulking fibers.

Examples of diamide salts include those described in U.S. PatentPublication No. 2004/0065423, filed Sep. 15, 2003, which is herebyincorporated in its entirety by reference. Non-limiting examples of suchsalts include mono- and distearamides of animoethylethalonalamine, whichmay be commercially known as Reactopaque 100, (Omnova Solutions Inc.,Performance Chemicals, 1476 J. A. Cochran By-Pass, Chester, S.C. 29706,USA and marketed and sold by Ondeo Nalco Co., with headquarters at OndeoNalco Center, Naperville, Ill. 60563, USA) or chemical equivalentsthereof. When such salts are used, about 0.025 to about 0.25 wt % byweight dry basis of the diamide salt may be used.

Other optional components include nitrogen containing compounds.Non-limiting examples of these include nitrogen containing organicspecies, for example oligomers and polymers which contain one or morequaternary ammonium functional groups. Such functional groups may varywidely and include, for example, substituted and unsubstituted amines,imines, amides, urethanes, quaternary ammonium groups, dicyandiamides,guanides, and the like. Illustrative of such materials are polyamines,polyethyleneimines, copolymers of diallyldimethyl ammonium chloride(DADMAC), copolymers of vinyl pyrrolidone (VP) with quaternizeddiethylaminoethylmethacrylate (DEAMEMA), polyamides, cationicpolyurethane latex, cationic polyvinyl alcohol, polyalkylaminesdicyandiamid copolymers, amine glycigyl addition polymers,poly[oxyethylene(dimethyliminio)ethylene(dimethyliminio)ethylene]dichlorides, guanidine polymers, and polymericbiguanides. Combinations of these nitrogen containing compounds arepossible. Some examples of these compounds are described in, forexample, U.S. Pat. No. 4,554,181, U.S. Pat. No. 6,485,139, U.S. Pat. No.6,686,054, U.S. Pat. No. 6,761,977 and U.S. Pat. No. 6,764,726, theentireties of each of which being hereby incorporated by reference.

The expandable microspheres may contain an expandable shell forming avoid inside thereof. The expandable shell may comprise a carbon and/orheteroatom containing compound. An example of a carbon and/or heteroatomcontaining compound may be an organic polymer and/or copolymer. Thepolymer and/or copolymer may be branched and/or crosslinked.

Expandable microspheres preferably are heat expandable thermoplasticpolymeric hollow spheres containing a thermally activatable expandingagent. Examples of expandable microsphere compositions, their contents,methods of manufacture, and uses can be found, in U.S. Pat. Nos.3,615,972; 3,864,181; 4,006,273; 4,044,176; and 6,617,364 which arehereby incorporated, in their entirety, herein by reference. Furtherreference can be made to U.S. Patent Publication Nos. 2001/0044477;2003/0008931; 2003/0008932; and 2004/0157057, which are herebyincorporated, in their entirety, by reference. Microspheres may beprepared from polyvinylidene chloride, polyacrylonitrile, poly-alkylmethacrylates, polystyrene or vinyl chloride.

Microspheres may contain a polymer and/or copolymer that has a Tgranging from −150 to +180° C., preferably from 50 to 150° C., mostpreferably from 75 to 125° C.

Microspheres may also contain at least one blowing agent which, uponapplication of an amount of heat energy, functions to provide internalpressure on the inside wall of the microsphere in a manner that suchpressure causes the sphere to expand. Blowing agents may be liquidsand/or gases. Further, examples of blowing agents may be selected fromlow boiling point molecules and compositions thereof. Such blowingagents may be selected from the lower alkanes such as neopentane,neohexane, hexane, propane, butane, pentane, and mixtures and isomersthereof. Isobutane is the preferred blowing agent for polyvinylidenechloride microspheres. Examples of coated unexpanded and expandedmicrospheres are disclosed in U.S. Pat. Nos. 4,722,943 and 4,829,094,which are hereby incorporated, in their entirety, by reference.

The expandable microspheres may have a mean diameter ranging from about0.5 to 200 microns, preferably from 2 to 100 microns, most preferablyfrom 5 to 40 microns in the unexpanded state and having a maximumexpansion of from about 1.5 and 10 times, preferably from 2 to 10 times,most preferably from 2 to 5 times the mean diameters.

In one embodiment, the expandable microspheres may be neutral,negatively or positively charged, preferably negatively charged.

If desired, one or more reducing agents may be optionally added toenhance the effect of the optical brighteners. Some examples of reducingagents are discussed in U.S. Patent Application Publication2007/0062653, incorporated herein by reference in its entirety. Ifutilized, one measure of an effective amount of reducing agent added tobleached pulp or paper product is that which enhances the brightness andresistance to thermal yellowing of the pulp or paper compared to pulp orpaper which is not treated with the reducing agents. Methods fordetermining brightness and resistance to thermal yellowing are known.

In one embodiment, a reducing agent is not used.

In one embodiment, a recording sheet prepared with the composition whichcontains a divalent metal salt, a complexing agent, and an opticalbrightening agent desirably exhibits an enhanced image dry time asdetermined by the amount of ink transferred from a printed to anunprinted portion of the recording sheet after rolling with a roller offixed weight. The “ink transfer”, that is defined as the amount ofoptical density transferred after rolling with a roller; it is expressedas a percentage of the optical density transferred to the unprintedportion of the recording sheet after rolling with a roller. The methodinvolves printing solid colored blocks on paper, waiting for a fixedamount of time, 5 seconds after printing, and then folding in half sothat the printed portion contacts an unprinted portion of the recordingsheet, and rolling with a 4.5 lb hand roller as for example roller itemnumber HR-100 from Chem Instruments, Inc., Mentor, Oh., USA. The opticaldensity is read on the transferred (OD_(T)), the non-transferred(OD_(O)) portions of the block, and an un-imaged area (OD_(B)) by areflectance densitometer (X-Rite, Macbeth. Etc.). The percenttransferred (“IT %”) is defined as IT%=[(OD_(T)−OD_(B))/(OD_(O)−OD_(B))]×100.

Given the teachings herein, the Hercules Sizing Test Value (“HST”) ofthe substrate prepared with the composition may be suitably selectedsuch that the recording sheet has a percent ink transferred (“IT %”)equal to or less than about 60. Preferably, the IT % is from 0% to about50%. More preferably, the IT % is from 0% to about 40%. Most preferably,the IT % is from 0% to about 30%.

In addition to improved image dry time, the recording sheets exhibitgood print quality. As used herein, print quality (PQ) is measured bytwo important parameters: print density and edge acuity. Print densityis measured using a reflectance densitometer (X-Rite, Macbeth. Etc.) inunits of optical density (“OD”). The method involves printing a solidblock of color on the sheet, and measuring the optical density. There issome variation in OD depending on the particular printer used and theprint mode chosen, as well as the densitometer mode and color setting.The printer is not particularly limited and may be, for example, an HPDeskjet 6122, manufactured by Hewlett-Packard, which uses a #45 (HPproduct number 51645A) black inkjet cartridge. The print mode isdetermined by the type of paper and the print quality selected. Thedefault setting of Plain Paper type and Fast Normal print quality printmode may be suitably selected. A suitable densitometer may be an X-Ritemodel 528 spectrodensitometer with a 6 mm aperture. The densitymeasurement settings may suitably be Visual color, status T, andabsolute density mode. An increase in print density may typically beseen when sufficient amounts of divalent water soluble metal salts areon the paper surface. In general, the target optical density for pigmentblack (“OD_(O)”) is equal to or greater than 1.30 in the standard (plainpaper, normal) print mode for the HP desktop ink jet printers that usethe most common black pigment ink (equivalent to the #45 ink jetcartridge). Preferably, the OD_(O) is equal to or greater than about1.40. More preferably, the OD_(O) is equal to or greater than about1.50. Most preferably, the OD is equal to or greater than about 1.60.

Recording sheets exhibit good edge acuity (“EA”). Edge acuity ismeasured by an instrument such as the QEA Personal Image Analysis System(Quality Engineering Associates, Burlington, Mass.), the QEA ScannerIAS,or the ImageXpert KDY camera-based system. All of these instrumentscollect a magnified digital image of the sample and calculate an edgeacuity value by image analysis. This value is also called edgeraggedness, and is defined in ISO method 13660. The method involvesprinting a solid line 1.27 millimeters or more in length, sampling at aresolution of at least 600 dpi. The instrument calculates the locationof the edge based on the darkness of each pixel near the line edges. Theedge threshold is defined as the point of 60% transition from thesubstrate reflectance factor (light area, R_(max)) to the imagereflectance factor (dark area, R_(max)) using the equationR₆₀=R_(max)−60% (R_(max)−R_(min)). The edge raggedness is then definedas the standard deviation of the residuals from a line fitted to theedge threshold of the line, calculated perpendicular to the fitted line.The value of edge acuity is preferably less than about 15. Preferably,the EA is less than about 12. More preferably, the EA is less than about10. Most preferably, the EA is less than about 8.

A recording sheet prepared using the composition may have any CIEwhiteness, but preferably has a CIE whiteness of greater than 70, morepreferably greater than 100, most preferably greater than 125 or evengreater than 150. The CIE whiteness may be in the range of from 125 to200, preferably from 130 to 200, most preferably from 150 to 200. TheCIE whiteness range may be greater than or equal to 70, 80, 90, 100,110, 120, 125, 130, 135, 140, 145, 150, 155, 160, 65, 170, 175, 180,185, 190, 195, and 200 CIE whiteness points, including any and allranges and subranges therein. Examples of measuring CIE whiteness andobtaining such whiteness in a papermaking fiber and paper made therefromcan be found, for example, in U.S. Pat. No. 6,893,473, which is herebyincorporated, in its entirety, herein by reference. Further, examples ofmeasuring CIE whiteness and obtaining such whiteness in a papermakingfiber and paper made therefrom can be found, for example, in U.S. PatentApplication No. 60/654,712 filed Feb. 19, 2005, and U.S. patentapplication Ser. No. 11/358,543 filed Feb. 21, 2006; Ser. No. 11/445,809filed Jun. 2, 2006; and Ser. No. 11/446,421 filed Jun. 2, 2006, whichare also hereby incorporated, in their entirety, herein by reference.

The recording sheet of the present invention may have any ISObrightness, but preferably greater than 80, more preferably greater than90, most preferably greater than 95 ISO brightness points. The ISObrightness may be preferably from 80 to 100, more preferably from 90 to100, most preferably from 95 to 100 ISO brightness points. This rangeinclude greater than or equal to 80, 85, 90, 91, 92, 93, 94, 95, 96, 97,98, 99, and 100 ISO brightness points, including any and all ranges andsubranges therein. Examples of measuring ISO brightness and obtainingsuch brightness in a papermaking fiber and paper made therefrom can befound, for example, in U.S. Pat. No. 6,893,473, which is herebyincorporated, in its entirety, herein by reference. Further, examples ofmeasuring ISO brightness and obtaining such brightness in a papermakingfiber and paper made therefrom can be found, for example, in U.S. PatentApplication Nos. 60/654,712 filed Feb. 19, 2005, and U.S. patentapplication Ser. No. 11/358,543 filed Feb. 21, 2006, which are alsohereby incorporated, in their entirety, herein by reference.

A recording sheet prepared in accordance with the present invention hasan improved print performance and improved runnability (e.g. print pressperformance). Print performance may be measured by determining improvedink density, dot gain, trapping, print contrast, and/or print hue, toname a few. Colors traditionally used in such performance tests includeblack, cyan, magenta and yellow, but are by no means limited thereto.Press performance may be determined by print contaminationdeterminations through visual inspection of press systems, blankets,plates, ink system, etc. Contamination usually includes fibercontamination, coating or sizing contamination, filler or bindercontamination, piling, etc. The recording sheet has an improved printperformance and/or runnability as determined by each or any one orcombination of the above attributes.

A recording sheet prepared using the composition may have any surfacestrength. Examples of physical tests of a substrate's surface strengththat also seem to correlate well with a substrate's print performanceare the IGT pick tests and wax pick tests. Further, both tests are knownin the art to correlate well with strong surface strength of recordingsheets. While either of these tests may be utilized, IGT pick tests arepreferred. IGT pick test is a standard test in which performance ismeasured by Tappi Test Method 575, which corresponds to the standardtest ISO 3873.

Paper substrates suitable for use herein may have any basis weight. Itmay have either a high or low basis weight, including basis weights ofat least 10 lbs/3000 square foot, preferably from at least 20 to 500lbs/3000 square foot, more preferably from at least 40 to 325 lbs/3000square foot. The basis weight may be at least 10, 20, 30, 40, 50, 60,70, 80, 90, 100, 125, 150, 175, 200, 225, 250, 275, 300, 325, 350, 375,400, 425, 450, 475, and 500 lbs/3000 square feet, including any and allranges and subranges therein.

The recording sheet may be suitably printed by generating images on asurface of the recording sheet using conventional printing processes andapparatus as for example laser, ink jet, offset and flexo printingprocesses and apparatus. In this method, the recording sheet isincorporated into a printing apparatus; and an image is formed on asurface of the sheet. The recording sheet may be printed with ink jetprinting processes and apparatus such as, for example, desk top ink jetprinting and high speed commercial ink jet printing. In one embodiment,an ink jet printing process is contemplated wherein an aqueous recordingliquid is applied to the recording sheet in an image wise pattern. Inanother embodiment, an ink jet printing process is contemplated whichincludes (1) incorporating into an ink jet printing apparatus containingan aqueous ink the recording sheet, and (2) causing droplets of the inkto be ejected in an image wise pattern onto the recording sheet, therebygenerating one or more images on the recording sheet. Ink jet printingprocesses are well known, and are described in, for example, U.S. Pat.No. 4,601,777, U.S. Pat. No. 4,251,824, U.S. Pat. No. 4,410,899, U.S.Pat. No. 4,412,224, and U.S. Pat. No. 4,532,530. In one embodiment, theink jet printing apparatus employs a thermal ink jet process wherein theink in the nozzles is selectively heated in an imagewise pattern,thereby causing droplets of the ink to be ejected onto the recordingsheet in imagewise pattern. The recording sheet can also be used in anyother printing or imaging process, such as printing with pen plotters,imaging with color laser printers or copiers, handwriting with ink pens,offset printing processes, or the like, provided that the toner or inkemployed to form the image is compatible with the recording sheet. Thedetermination of such compatibility is easily carried out given theteachings herein combined with the ordinary skill of one knowledgeablein the printing art.

The relevant contents of each of U.S. Provisional Patent Application60/759,629, filed Jan. 17, 2006; U.S. Provisional Patent Application60/853,882, filed Oct. 24, 2006; U.S. Provisional Patent Application60/759,630, filed Jan. 17, 2006; U.S. patent application Ser. No.10/662,699, filed Sep. 15, 2003, and published Apr. 8, 2004, as U.S.Patent Application Publication No. 2004/0065423; U.S. patent applicationSer. No. 11/655,004, filed Jan. 17, 2007, and published Feb. 14, 2008,as U.S. Patent Application Publication 2008/0035292 are independentlyincorporated herein by reference.

The entire contents of “Handbook for Pulp and Paper Technologists” by G.A. Smook (1992) Angus Wilde Publications, is incorporated herein byreference.

All of the references, as well as their cited references, cited hereinare hereby incorporated by reference with respect to relative portionsrelated to the subject matter of the present invention and all of itsembodiments.

EXAMPLES

The present invention may be described in further detail with referenceto the following examples. The examples are intended to be illustrative,but the invention is not considered as being limited to the materials,conditions, or process parameters set forth in the examples. All partsand percentages are by unit weight unless otherwise indicated.

Example 1 Ca(II) Decreases OBA Optical Properties

A lab-scale puddle size press was used for the treatment on a Mill Aproduced base paper. The size press formulation was conventionallyrepresented on the basis of each 100 lb of starch. In this experiment,40 Lb of OBA (Clariant Leucophor BCW) was used per 100 Lb of cookedethylated starch (Penford Gum 280, cooked at 18% solids). In one case,15 Lb of CaCl₂ was added. In another case, no Ca(II) was used.

FIG. 1 and the tables below show the effect of Ca(II) on CIE whiteness.It is quite clear, with these two runs (repeated a few days apart), thatthe presence of Ca(II) significantly decreased the paper opticalproperties.

Bench-top size-press, 40 Lb OBA per 100 Lb of ethylated starch.brightness whiteness No Ca(II) 94.2 152.1 With Ca(II) 93.9 147.8

Another run, at 40 # of OBA per 100 lb of ethylated starch. whiteness NoCa(II) 152.4 With Ca(II) 148.3

Example 2 Impact of Complexing Agents on CIE Whiteness

A lab-scale size press treatment was conducted, similar to Example 1. Inthe formulation, 40 Lb of OBA (Leucophore BCW) and 5 Lb of complexingagents were used per 100 Lb of ethylated starch. In one case, 15 Lb ofCaCl2 was added in the formulation. In another case, no CaCl₂ was added.

The results (as shown in the following tables and graphically in FIG. 2)indicate that complexing agents may improve whiteness of paper.Especially in the presence of Ca(II), EDTA complexes with Ca(II)improves whiteness, while EDTA with no Ca(II) does not show a beneficialeffect.

With Ca(II) Brightness Whiteness Ca(II) Control 93.9 147.8 5# EDTA inCa(II) 93.8 149.3 5# PEG in Ca(II) 93.9 149.4 5# DTPA in Ca(II) 93.8149.3 5# PSS in Ca(II) 93.7 148.9

Without Ca(II) Brightness Whiteness Control-without Ca(II) 94.5 152.0 5#EDTA without Ca(II) 93.0 142.5 5# PEG without Ca(II) 94.2 152.5 5# DTPAwithout Ca(II) 94.5 153.4 5# PSS without Ca(II) 94.5 152.9

Example 3 Complexing Agents with Ca(II) on Ink-Jet Printing Properties

Soluble Ca(II) is known to improve ink-jet printing properties, such asink density. In this experiment, treated paper samples as in Example 2were tested for printing properties. It is shown clearly that addingcomplex agents with Ca(II) did not negatively impact the printingproperties. The results are illustrated in the following table andgraphically in FIG. 3 and FIG. 4.

Ink Density % Ink-transfer/removal Control-without Ca(II) 1.38 26.6%Ca(II) Control 1.55 23.2% 5# EDTA in Ca(II) 1.54 19.1% 5# PEG in Ca(II)1.51 13.7% 5# DTPA in Ca(II) 1.54   19% 5# PSS in Ca(II) 1.54   11%

Example 4 Dose-Response of EDTA in Ca(II)

In a size-press experiment as by Example 1 with 40 Lb of OBA (LeucophoreBCW), two doses of EDTA were added for comparison. The dose response ofEDTA is illustrated in the following table and graphically in FIG. 5.

whiteness Ca(II) Control 148.3 1# EDTA in Ca(II) 149.3 3# EDTA in Ca(II)150.3

Example 5 Pilot Scale Size Press Experiment, EDTA (Versene-100) vs.Nalco's Extra White

A pilot scale size press experiment was conducted to evaluate theeffectiveness of EDTA (Dow's Versene-100). Another objective was toobtain a side-by-side comparison with a commercial additive (Nalco'sExtra White™ NW-3).

Mill B base paper was used, with size-press running at ˜100 ft/min, 150°F., pH˜7, pick-up of about 100 Lb starch/ton of paper:

-   -   (1) In the control run, 15 Lb of CaCl₂ per 100 Lb of starch was        used. The OBA (Leucophor BCW) loadings were respectively 0, 15,        30, 45, 60 Lb OBA per 100 Lb ethylated starch.    -   (2) In the Versene (EDTA) run, 4 Lb of Versene-100 (per 100 Lb        starch) were added to the control run case, at various OBA        loadings.    -   (3) In the EW run, 5 Lb of Extra White (per 100 Lb starch) were        added to the control run, at various OBA loadings.    -   (4) All the treated sheets were then heated by running through        sheet dryer at 235 F.

The results are shown in FIG. 6 and FIG. 7. It is shown that EDTA(Versene) may improve optical properties—or it may significantly lowerthe amounts of OBA necessary to achieve the same target whiteness orbrightness. It was found that Nalco's Extra White encounteredincompatibility and size press runnability issues with the Ca(II)chemistry, and no benefit in optical properties were observed.

Example 6 Pure Solution Soaking Experiment

Base paper sheets were dipped into the aqueous solution containing OBA,CaCl₂ and complexing agents. The concentration was adjusted so that thepick-up will correspond to similar size press formulation ratios (butwithout starch).

The tables below show the results from:

-   -   4 Lb/ton paper complexing agent pick-up    -   15 Lb/ton paper CaCl2 pick-up    -   OBA pick-up of 0, 10, 20, 40, 60, and 80 Lb/ton paper    -   Leucophor SUS and Leucophor BCW were used as OBA.

From the results, which are shown in the following tables andgraphically in FIGS. 8, 9, and 10, it is obvious that the whiteness gaincan be confirmed for the complexing agents. It was also observed thatFAS resulted in substantial brightness gain.

Leucophor SUS - Whiteness Gain by Complexing Agents Control OBA #/ w/Ton CaCl2 EDTA DTPA AR-490 PSS FAS Cartacoat 0 118.4 117.5 118.1 117.9118.0 120.1 117.6 10 143.5 143.2 142.6 141.3 143.2 146.7 143.3 20 147.0148.6 147.8 147.2 149.0 150.2 149.2 40 149.5 150.4 150.7 149.8 150.6151.8 151.1 60 149.9 150.5 150.7 150.3 150.9 151.4 151.6 80 149.6 149.6149.8 149.2 149.6 150.0 150.5

Leucophor SUS-Brightness Gain by FAS OBA #/Ton Control w/ CaCl2 FAS 086.3 87.5 10 89.5 91.1 20 90.4 91.6 40 90.6 91.9 60 90.4 91.8 80 90.691.8

Leucophor BCW-Brightness Gain by FAS OBA #/ton Control w/ CaCl2 FAS 086.3 87.5 10 89.0 90.7 20 89.7 91.2 40 90.2 91.4 60 90.2 91.5 80 89.991.4

Example 7 UV and Photo Stability Due to Complexing Agents in Ca(II)

Lab scale size press treatments were carried out as in Example 1. Thetreated paper sheets were then subjected to aging conditions:

-   -   (1) UV aging was conducted inside an enclosed lightbox with UV        (dark light) onto the felt side for 24 hours.    -   (2) Photo aging was conducted inside an enclosed lightbox with        Daylight (fluorescent bulb) onto the felt side for 24 hours.    -   (3) The paper optical properties before and after exposure were        tested.

EDTA-Ca(II), DTPA-Ca(II), FAS-Ca(II), (But no by PEG-Ca(II) itself); PEGsynergy:PEG/FAS-Ca(II), PEG/EDTA-Ca(II), PEG/DTPA-Ca(II). FIG. 11 showsfelt side sheet brightness and whiteness data before and after UV anddaylight exposure. FIG. 12 shows a synergy effect of addition of PEG toCa(II) on UV and photo stability before and after 24 hour exposure to UVand daylight.

Example 8 Ionic Liquid is Effective as Complexing Agent

Lab scale size press treatment was carried out as by Example 1. In thesize press formulation, 15 Lb of CaCl₂ and 40 Lb of OBA (Leucophor BCW)were used on the basis of 100 Lb of starch per ton of paper.

An Ionic Liquid, BMIM (1-butyl-3-methyl-imidazolium-thiocyanate), wasused as an additive of interest and was compared with sodium EDTA(Versene-100) and tetramethyl ammonium EDTA. All these chemicals wereapplied at 5 Lb per 100 Lb starch.

It was surprisingly found that an ionic liquid may act as a complexingagent and improve the paper optical properties. The results are shown inthe table below.

Treated Sheet CIE Whiteness Control Ca(II) 145.4 EDTA Ca (II) 146.9Tetramethyl ammonium EDTA Ca(II) 146.3 BMIM Ca(II),1-butyl-3-methyl-imidazolium- 147.1 thiocyanate

Ink-Jet printing properties were also tested in some of the papersamples, and were compared with the CaCl₂ control as well as acommercial HP Ca(II) paper control. The results are shown in the tablebelow. All the printing properties are within the specification targets.

HP DJ6122 HP DJ6122 HP B9180 Black Dry time Color Density % transferGammut Control Ca(II) 1.49 2% 214162 1.51 1% 215187 EDTA Ca (II) 1.50 2%213771 1.50 2% 212630 BMIM Ca(II), 1-butyl-3-methyl- 1.51 7% 212667imidazolium-thiocyanat 1.50 10% 212183 A Commercial HP Paper 1.48 13%206344 1.51 13% 210351

As used throughout, ranges are used as a short hand for describing eachand every value that is within the range, including all subrangestherein.

Numerous modifications and variations on the present invention arepossible in light of the above teachings. It is, therefore, to beunderstood that within the scope of the accompanying claims, theinvention may be practiced otherwise than as specifically describedherein.

1. A recording sheet, comprising: a paper substrate comprising aplurality of cellulosic fibers; and a composition, comprising: awater-soluble salt of a divalent metal; a complexing agent having anaffinity for the divalent metal; and an optical brightening agent,wherein said complexing agent is selected from the group consisting oforganic phosphonate, phosphate, carboxylic acid, dithiocarbamate,ethylenediaminetetraacetic acid, ethylenediaminetetraacetic acid salt,diethylenetriaminepentaacetic acid, diethylenetriaminepentaacetic acidsalt, diethylene-triamine-pentamethylene phosphonic acid,diethylene-triaminepentamethylene phosphonic acid salt, crown ether,ethylenediaminetetraacetic acid, ethylenediaminetetraacetic aciddisodium salt, ethylenediaminetetraacetic acid tetrasodium salt,ethylenediaminetetraacetic acid trisodium salt,ethylenediaminetetraacetic acid disodium magnesium salt,ethylenediaminetetraacetic acid disodium calcium salt,ethylenediaminetetraacetic acid diammonium salt,ethylenediaminetetraacetic acid dipotassium salt,ethylenediaminetetraacetic acid tripotassium salt,ethylenediaminetetraacetic acid dilithium salt,ethylenediaminetetraacetic acid tetramethylammonium salt,ethylenediaminetetraacetic acid calcium salt, ethylenediaminetetraaceticacid magnesium salt, ethylenediaminetetraacetic acid aluminum salt,polyacrylic acid, polyacrylic acid salt, polysorbate, poly-4-styrenesulfonic acid salt, glycerol formal, formamidinesulinic acid, sodiumhypophosphite, potassium hypophosphite, calcium hypophosphite, organicphosphonate, organic phosphate, dithiocarbamate, sorbitol, sorbic acid,cellulose ether, ionic liquids,1-butyl-3-methyl-imidazolium-thiocyanate, alkyl imidazoliums1-ethyl-3-methylimidazolium thiocyanate, 1-ethyl-3-methylimidazoliumacetate, 1-ethyl-3-methylimidazolium methyl sulfate, methyl imidazolium,salts thereof, or a combination thereof.
 2. The recording sheet of claim1, wherein the salt is calcium (II) salt.
 3. The recording sheet ofclaim 1, wherein the salt comprises a combination of salts of divalentmetals.
 4. The recording sheet of claim 1, which further comprisesstarch, and wherein the complexing agent is present in an amount rangingfrom about 0.01 Lb/100 Lb starch to about 100 Lb/100 Lb starch.
 5. Therecording sheet of claim 1, which further comprises a sizing, agent, andwherein the optical brightening agent is present in an amount rangingfrom about 10 to 100 pounds per 100 pounds of sizing agent.
 6. A methodfor making the recording sheet according to claim 1, comprising:contacting the paper substrate comprising the plurality of cellulosicfibers; and a composition, comprising: the water-soluble salt of adivalent metal; the complexing agent having an affinity for the divalentmetal; and the optical brightening agent; to produce the recordingsheet.
 7. The method of claim 6, wherein the contacting is carried outat a size press.
 8. The method of claim 6, wherein the divalent metal isselected from the group consisting of calcium, magnesium, barium, zinc,or a combination thereof.
 9. The recording sheet of claim 1, wherein thesalt is present in an amount of about 0.02 g/m² to about 4 g/m² of therecording sheet.
 10. The recording sheet of claim 1, wherein thedivalent metal is selected from the group consisting of calcium,magnesium, barium, zinc, or a combination thereof.
 11. The recordingsheet of claim 1, wherein the complexing agent is present in an amountranging from about 0.01 Lb/ton of recording sheet to about 100 Lb/ton ofrecording sheet.
 12. The recording sheet of claim 1, wherein the opticalbrightening agent is present in an amount ranging from about 0.005 toabout 4 weight percent based on the weight of the recording sheet.